1. Field of the Invention
The present invention relates to a diplexer module including a switch, and more specifically, relates to a diplexer module including a switch that has excellent isolation characteristics between transmission and reception sides.
Furthermore, the present invention relates to a diplexer module, and more specifically, relates to a diplexer module that has excellent isolation characteristics between transmission and reception sides.
2. Description of the Related Art
Data over cable service interface specifications (DOCSIS) (registered trademark) is defined as a standard of high-speed data communication using a cable television line, and data communication services based on the standard are used in many countries.
The DOCSIS has been improved many times and version upgrading has been provided. Further version upgrading of the DOCSIS is planned in the future.
In the version upgrading of the DOCSIS, a communication frequency is changed in some cases.
The DOCSIS requires a communication apparatus of a new version to be capable of being used in an old version, in other words, requires the communication apparatus of the new version to support a communication frequency of the old version when the communication frequency is changed in the version upgrading. That is to say, the DOCSIS requires the new communication apparatus to be capable of being used in both of a service area in which the old version is used and a service area in which the new version is used with compatibility. Therefore, when it is desired that one communication apparatus is used to perform bidirectional communication with a plurality of communication frequencies as in communication based on the DOCSIS, a diplexer module including a switch using a plurality of diplexers supporting the DOCSIS of the latest version and the DOCSIS of the old version in a switching manner is used for a set top box connecting an external antenna or cable and an internal (in-room) communication line in some cases.
Japanese Unexamined Patent Application Publication No. 2015-111803 discloses such a diplexer module that includes a switch.
FIG. 8 illustrates a diplexer module (communication module) 1100 including a switch as disclosed in Japanese Unexamined Patent Application Publication No. 2015-111803.
The diplexer module including the switch 1100 includes a plurality of transmission and reception systems having different frequency bands and also supports the global positioning system (GPS) and the WiFi (registered trademark) communication. Hereinafter, the diplexer module including the switch 1100 is described for only portions that are used as references for a diplexer module including a switch according to the invention.
The diplexer module 1100 includes a switch 101. A fixed terminal of the switch 101 is connected to an antenna 102. One switching terminal of the switch 101 is connected to a first diplexer 103 and another switching terminal of the switch 101 is connected to a second diplexer 104.
The first diplexer 103 includes a first transmission filter 103a and a first reception filter 103b. In the same manner, the second diplexer 104 includes a second transmission filter 104a and a second reception filter 104b. 
Furthermore, the diplexer module 1100 includes a radio frequency integrated circuit (RFIC) 105 as a portion of a high-frequency circuit of a communication apparatus. The RFIC 105 includes a plurality of TX terminals and a plurality of RX terminals. Normally, related TX terminals of an RFIC are adjacent to each other and related RX terminals thereof are adjacent to each other. Also for the RFIC in the diplexer module 1100, the related TX terminals thereof are adjacent to each other and the related RX terminals thereof are adjacent to each other.
One TX terminal of the RFIC 105 is connected to the first transmission filter 103a of the first diplexer 103 and another adjacent TX terminal of the RFIC 105 is connected to the second transmission filter 104a of the second diplexer 104. In the same manner, one RX terminal of the RFIC 105 is connected to the first reception filter 103b of the first diplexer 103 and another adjacent RX terminal of the RFIC 105 is connected to the second reception filter 104b of the second diplexer 104.
The diplexer module 1100 disclosed in Japanese Unexamined Patent Application Publication No. 2015-111803 switches the switch 101, thus performing communication with a first frequency band using the first diplexer 103 and communication with a second frequency band using the second diplexer 104 in a switching manner.
In the diplexer module 1100 disclosed in Japanese Unexamined Patent Application Publication No. 2015-111803, as illustrated in FIG. 8, a point P at which signal lines intersect with each other is provided between the first diplexer 103 and the second diplexer 104 and the RFIC 105. To be more specific, a reception signal line connecting the first reception filter 103b of the first diplexer 103 and the RX terminal of the RFIC 105 and a transmission signal line connecting the second transmission filter 104a of the second diplexer 104 and the TX terminal of the RFIC 105 intersect with each other at the point P.
FIG. 9A is a schematic circuit diagram of the diplexer module 1100. FIG. 9B is a schematic circuit diagram of a variation of the diplexer module 1100, which has been arbitrarily produced by the inventors of the present invention. As shown in FIG. 9A, it is considered that the point P at which the signal lines intersect with each other occurs in the diplexer module 1100 because the related TX terminals of the RFIC 105 are adjacent to each other and the related RX terminals thereof are adjacent to each other. As in the variation of the diplexer module 1100 as illustrated in FIG. 9B, when a second switch SW2 and a third switch SW3 are additionally added, the first transmission filter 103a and the second transmission filter 104a are connected to the TX terminal of the RFIC 105 with the second switch SW2 interposed therebetween, and the first reception filter 103b and the second reception filter 104b are connected to the RX terminal of the RFIC 105 with the third switch SW3 interposed therebetween, the point P at which signal lines intersect with each other also occurs in the same manner.
There is a risk that the intersection of the signal lines at the point P in the diplexer module 1100 disclosed in Japanese Unexamined Patent Application Publication No. 2015-111803 generates signal interference and causes deterioration in communication quality of the module 1100. For this reason, the intersection of the signal lines is extremely disadvantageous. That is to say, there is a risk that a transmission signal directing to the second transmission filter 104a of the second diplexer 104 from the TX terminal of the RFIC 105 is mixed into a reception signal directing to the RX terminal of the RFIC 105 from the first reception filter 103b of the first diplexer 103 at the point P. In the same manner, there is a risk that the reception signal directing to the RX terminal of the RFIC 105 from the first reception filter 103b of the first diplexer 103 is mixed into the transmission signal directing to the second transmission filter 104a of the second diplexer 104 from the TX terminal of the RFIC 105 at the point P. In these interferences, when a portion of the reception signal is mixed into the transmission signal, it can be attenuated by the second transmission filter 104a and therefore, no problems arise in this case. On the other hand, when a portion of the transmission signal is mixed into the reception signal, as illustrated in FIGS. 9A and 9B, an S/N ratio is deteriorated because not only an unnecessary signal can be attenuated only in the RFIC 105 but also the transmission signal has a larger amplitude than the weak reception signal, resulting in a significant problem that reception sensitivity is deteriorated.